The present invention relates to a large scale integrated circuit (IC) package mounted with a plurality of IC chips.
One example of conventional large scale integrated circuit (LSI) packages is proposed in a paper entitled "A Comparison of Thin Film, Thick Film, and Co-Fired High Density Ceramic Multilayer with the Combined Technology: T&T HDCM" by Dr. M. Terasawa et al., published in the The International Journal for Hybrid Micro-electronics, Vol. 6, No. 1, October 1983, Pages 607 to 615. Since the alumina (Al.sub.2 O.sub.3) ceramic substrate in such a conventional package is formed by laminating and sintering alumina green sheets, it can be made no thinner than 0.1 to 0.3 mm. As a result, the characteristic impedance of signal wiring cannot be reduced below a certain limit value. Therefore, if the impedance of circuit elements to be mounted is below this limit value, it will be impossible to achieve impedance matching and invite a deterioration in crosstalk characteristic. Another disadvantage is that those ICs mounted on the LSI package might cause the characteristic impedance of the signal wiring to deviate from its designed value.
Furthermore, an organic material used for the insulating layer of the package is much less hard than an inorganic material. Consequently, if wires for connection to IC's and the like are connected to pads on the substrate by a thermal compression bonding technique, which involves the application of a high temperature and high pressure, denting or otherwise deforming the organic material is likely to reset and make normal bonding impossible. Further, such dent or deformation affects the wiring layer underneath the organic material so that faulty wiring occurs. Accordingly, in this type of package, the IC chips are ordinarily connected by soldering by way of leadless chip carriers (LCCs). The mounting using the LCCs does not allow higher mounting density.